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Handwritten Recognition using Deep Learning with R

3.
Introduction
In the past 10 years, machine learning and Artificial Intelligence (AI) have shown
tremendous progress
The recent success can be attributed to:
Explosion of data
Cheap computing cost - CPUs and GPUs
Improvement of machine learning models
Much of the current excitement concerns a subfield of it called “deep learning”.
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5.
Neural Networks
Deep Learning is primarily about neural networks, where a network is an
interconnected web of nodes and edges.
Neural nets were designed to perform complex tasks, such as the task of placing
objects into categories based on a few attributes.
Neural nets are highly structured networks, and have three kinds of layers - an input,
an output, and so called hidden layers, which refer to any layers between the input and
the output layers.
Each node (also called a neuron) in the hidden and output layers has a classifier.
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7.
Neural Network: Forward Propagation
The input neurons first receive the data features of the object. After processing the
data, they send their output to the first hidden layer.
The hidden layer processes this output and sends the results to the next hidden layer.
This continues until the data reaches the final output layer, where the output value
determines the object’s classification.
This entire process is known as Forward Propagation, or Forward prop.
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8.
Neural Network: Backward Propagation
To train a neural network over a large set of labelled data, you must continuously
compute the difference between the network’s predicted output and the actual output.
This difference is called the cost, and the process for training a net is known as
backpropagation, or backprop
During backprop, weights and biases are tweaked slightly until the lowest possible cost is
achieved.
An important aspect of this process is the gradient, which is a measure of how much
the cost changes with respect to a change in a weight or bias value.
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9.
The 1990s view of what was wrong with
back-propagation
It required a lot of labelled training data
Almost all data is unlabeled
The learning time did not scale well
It was very slow in networks with multiple hidden layers.
It got stuck at local optima
These were often surprisingly good but there was no good theory
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10.
Deep Learning
Deep learning refers to artificial neural networks that are composed of many layers.
It’s a growing trend in Machine Learning due to some favorable results in applications
where the target function is very complex and the datasets are large.
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11.
Deep Learning: Benefits
Robust
No need to design the features ahead of time - features are automatically learned to be optimal for
the task at hand
Robustness to natural variations in the data is automatically learned
Generalizable
The same neural net approach can be used for many different applications and data types
Scalable
Performance improves with more data, method is massively parallelizable
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12.
Deep Learning: Weaknesses
Deep Learning requires a large dataset, hence long training period.
In term of cost, Machine Learning methods like SVMs and other tree ensembles are
very easily deployed even by relative machine learning novices and can usually get you
reasonably good results.
Deep learning methods tend to learn everything. It’s better to encode prior
knowledge about structure of images (or audio or text).
The learned features are often difficult to understand. Many vision features are also
not really human-understandable (e.g, concatenations/combinations of different
features).
Requires a good understanding of how to model multiple modalities with
traditional tools.
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17.
MNIST Handwritten Dataset
The MNIST database consists of handwritten digits.
The training set has 60,000 examples, and the test set has 10,000 examples.
The MNIST database is a subset of a larger set available from NIST. The digits have
been size-normalized and centered in a fixed-size image
For this demo, the Kaggle pre-processed training and testing dataset were used. The
training dataset, (train.csv), has 42000 rows and 785 columns.
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18.
Demo
The sourcecode can be accessed from here
https://github.com/kuanhoong/myRUG_DeepLearning
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